This invention relates to an apparatus for photometrically analysing liquid samples.
The successive analysis of a large number of samples is faced with the difficulty of preventing the measurement in progress from being spoiled by residues remaining in the apparatus after measurement of the preceding sample. For example, the concentration or the composition of a sample may be modified by these residues and produce an error in the resulting measurement. This is in particular the case for apparatus measuring the properties of samples by photometry.
In a known apparatus of this type sold under the reference XP-2000 by Skan AG of 4009 Basel-Allschwil, Switzerland, the photometric measurement is carried out while the sample is located in a chamber isolated from ambient light. This chamber is defined in a plate screwed to the front of a housing containing a photomultiplier and appropriate electronic circuits which transform the signal supplied by the photomultiplier into data which the user can exploit. The apparatus in question is intended typically for the measurement of bioluminescence produced by the reaction of an enzyme on a liquid sample mixed with a certain quantity of living organisms such as bacteria. However, very similar difficulties may be encountered in the analysis of a liquid by for example measuring its transparency to light. The photomultiplier thus for example serves to measure the light which reaches it through the liquid from a light source opposite the photomultiplier.
A detailled description of the method of analysis by bioluminescence is found in an article by N. Maire in the publication "Soil Biol. Biochem." vol. 16, no. 4, pp 361-366, 1984. In summary, it involves analysing a medium, such as soil, by first extracting the ATP molecule from the medium's cells by rupturing the cells' walls and then photometrically measuring the molecule by an enzymatic bioluminescence reaction. This is made possible because the intensity of the light emitted during this reaction is directly proportional tot he concentration of ATP and because this concentration is representative of the biological activity of the soil sample under examination, ATP being a mononucleotide of the metabolism that is found in all living organisms and which ensures the transmission or the storage of energy in most biochemical reactions taking place in living cells (respiration, fermentation, photosynthesis, etc.)
To obtain a faithful evaluation of bioluminescence, it is nonetheless necessary to carefully avoid contamination of a sample during analysis by a sample which has just been analysed.
In the known apparatus mentioned above, this requirement is satisfied by rinsing the measurement cell with a rinsing liquid. But to accomplish this, the assembly plate must be taken off the capsule, the cell removed from the latter and rinsed, followed by a reassembly operation. This method therefore does not lend itself to rapid and automatic processing of a large number of samples.